Is this an Alternator issue?

[markcro]

This evening when out, the car got very lumpy when sitting in traffic, and then was trying to cut out. I had trouble keeping her going. But I found if I turned off all electrics she then ran fine, and got her home.
Anyway I did some testing at home:

- with full lights on, fan, interior fan she ran like a bag of bolts, very reluctant to rev and was miss firing.
- Turn everything off and she then ran near perfect. A little hesitation a few times when blipping the throttle but nearly fine.
- I ran a cable from the battery directly to the coil and she ran 100% with and without all electrics on.

- I stuck a multimeter on the coil to see what voltage it was getting with all of the electrics on. Initially it looked good at about 13v. But then it slowly started dropping away - 12-11.5-11-10.5 and at this point the engine starts getting really lumpy and tries to stall.
- Quickly turning off all the electrics and it the voltages jumps back up to about 12.5. v.

But while doing all of this the is no "alternator" warning light showing on the dash and all the lights are perfectly bright. What do you think? Alternator on the way out/ worsened when under the bonnets gets hot? Any other culprits that it could be?
But if the voltage to the coil was dropping away, why doesn't the lights dim/ fans slow?

If the alternator; are there any modern upgrades to replace it? I.e. from a modern scrapped car?  Or just get the original alternator rebuilt or replace?

Cheers!

[Nick Jones]

No, more likely a wiring or ignition switch problem

"- I ran a cable from the battery directly to the coil and she ran 100% with and without all electrics on"  This is were you proved it.  

The volt drop is somewhere in the ignition controlled circuit and the ignition switch also controls the fan, wipers, brake lights, instruments and overdrive.  The lights are not ignition controlled so won't be affected.  The voltage drop shows that a wiring joint or switch contact is heating up and it's resistance increasing.  Ignition switch would be my prime suspect.

Nick

[Nick Jones]

No, more likely a wiring or ignition switch problem

"- I ran a cable from the battery directly to the coil and she ran 100% with and without all electrics on"  This is were you proved it.  

The volt drop is somewhere in the ignition controlled circuit and the ignition switch also controls the fan, wipers, brake lights, instruments and overdrive.  The lights are not ignition controlled so won't be affected.  The voltage drop shows that a wiring joint or switch contact is heating up and it's resistance increasing.  Ignition switch would be my prime suspect.

Nick

[Nick Jones]

No, more likely a wiring or ignition switch problem

"- I ran a cable from the battery directly to the coil and she ran 100% with and without all electrics on"  This is were you proved it.  

The volt drop is somewhere in the ignition controlled circuit and the ignition switch also controls the fan, wipers, brake lights, instruments and overdrive.  The lights are not ignition controlled so won't be affected.  The voltage drop shows that a wiring joint or switch contact is heating up and it's resistance increasing.  Ignition switch would be my prime suspect.

Nick

[markcro]

Cheers Nick. As it happens I have a new ignition switch sitting in a box so I'll swap it out. I bet that it is a balls of a job?!! All this summer it seems that each "small" job has turned into a balls of a job! Ah well, see will be running sweet for next summer.